In recent years, there has been active study of technical approaches for achieving a high transmission rate using a high-frequency radio band in cellular mobile communication systems typified by mobile telephones (see Non-Patent Document 1, for example). An example of such study relates to MIMO (Multiple Input Multiple Output) transmission and the like in which a plurality of data sequences are transmitted from a plurality of transmitting antennas, and signals received using a plurality of receiving antennas are separated into data sequences and decoded.
However, when a high-frequency radio band is used, attenuation due to transmission distance increases compared to the case where a low-frequency radio band is used, and the rectilinear property of the radio waves becomes more significant. In other words, radio waves that pass around buildings and other obstacles are weakened, and therefore the areas where the high transmission rate can be expected are limited to relatively short distances. There must therefore be more base station apparatuses provided within the system. Providing base station apparatuses costs corresponding money, and there is therefore a significant need for a technique that realizes a high transmission rate while suppressing an increase in the number of base station apparatuses to be provided.
In an example of a conventional mobile communication system, the coverage area of a base station apparatus is substantially enlarged by using a relay station apparatus for relaying a radio signal from a transmitting apparatus to a receiving apparatus (see Patent Document 1, for example).    Patent Document 1: Japanese Patent Application Laid-Open No. 2002-330112 Non-patent Document 1: “Investigation of Pilot Channel Structure for VSF-OFCDM Broadband Wireless Access,” The Technical Report of the IEICE of Japan, RCS2002-169 (2002-10).